IL-1RA reactivity correlates with multiorgan involvement of IgG4-RD and is expressed in tissue lesions of IgG4-RD patients. A, Number of affected organs in IgG4-RD patients either positive or negative for IgG4 anti-IL-1RA autoantibodies from the validation cohort. B and C, IL-1RA immunofluorescence in tissue-biopsy samples from four patients with IgG4-RD and one patient with Sjögren’s syndrome. IL-1RA (red) and DAPI (blue) staining in biopsied kidney, lymph node, lacrimal gland, and salivary gland tissues from four patients with IgG4-RD and salivary gland tissue from one patient with Sjögren’s syndrome (B). Quantification of IL-1RA staining in tissue biopsies from the patients described (C). Data represent percentage of subjects with and without anti-IL-1RA autoantibodies of ≥2 independent experiments (A) or means ± SD of the cell counts positive for IL-1RA per mm^2 of five fields per tissue sample (C). *P < 0.05, **P < 0.01 by Mann-Whitney U-tests.